Re: [m2e-users] The mess that is M2E connectors

[Kathryn Huxtable <kathryn@xxxxxxxxxxxxxxxxxxx>]

I agree strongly. There may be reasons why the M2E developers have done what they have, but the effect is to make me wonder if I'd be happier using IntelliJ. Or dumping Maven. Nah, it'd be IntelliJ.

-K

On Aug 27, 2011, at 7:52 PM, Jochen Wiedmann wrote:

> Hi,
> 
> just like to point your attention to
> 
> http://grumpyapache.blogspot.com/2011/08/mess-that-is-m2e-connectors.html
> 
> It should be better to read there, but I am quoting for the sake of
> discussion below:
> 
> 
> The mess that is m2e connectors
> 
>    Warning: The following is most likely stubborn,
> unreasonable,one-sided, and ignores a lot of facts, of which I am
> unaware.
> 
> I am an Eclipse user since approximately 10 years. I am also a user of
> Maven 2 since may be 4-5 years. As a consequence I am also using the
> former M2Eclipse (an Eclipse Plugin for using Maven as the Eclipse
> Builder) since its early days. While I am quite happy with Eclipse and
> Maven, the experience with M2Eclipse has never been free from
> annoyance and fights. To be honest, it has always been hard to
> convince my colleagues to use it. And I fear that battle is lost now.
> I wasn't the one loosing it: The decisive strike was administrated by
> M2E itself...
> 
> M2Eclipse has recently been moved to the Eclipse Foundation. It is now
> called M2E, lives at eclipse.org and can be installed from within
> Eclipse Indigo as a standard plugin, just like CDT, or WTP, which is,
> of course, a good thing.
> 
> So, when Indigo was published (together with M2E 1.0 as a simultaneous
> release), I rushed to load it down in the hope of a better user
> experience. But the first thing I noted was: M2E was showing errors in
> practically every POM I have ever written, and there are quite a few
> of them, including those of several Apache projects and those at work.
> So,as a first warning:
> 
> M2E 1.0 is incompatible with its predecessors. If you want to carry on
> using it without problems, don't upgrade to Indigo, or try using an
> older version of M2Eclipse with it (I haven't tried, whether that
> works. The reason for this intentional incompatibility (!) are the
> so-calles M2E connectors, which, I am sure, have driven a lot of
> people to madness since their invention. In
> whathttp://www.blogger.com/img/blank.gif follows I'll try to outline
> my understanding of what the connectors are and why I do consider them
> a real, bloody mess.
> 
> I am still not completely sure, what problem the connectors ought to
> solve, but from my past experiences I guess something like this:
> 
> M2E allows you to run Maven manually. You can invoke a goal like "mcn
> install" from within Eclipse just as you would do it from the command
> line. That works (and always worked) just fine. Unfortunately, Maven
> is also invoked automagically from M2E whenever Eclipse builds the
> project, for example after a clean. In such cases M2E acts as an
> "Eclipse Builder". It is these latter invocations that people have
> always had problems withand that the connectors should hanle better.
> First of all, what are these problems?
> 
>    Builders can be invoked quite frequently. If automatic builds are
> enabled and you are saving after every 10 keys presse, the builders
> can be invoked every 20 seconds or so.
>    The UI is mainly locked while a builder is running. In conjunction
> with the frequent invocation that means that the UI can be locked 80%
> of the time, ehich a human developer considers extremely painful, in
> particular, if the builder invokes Maven, which can take quite some
> time.
>    Some Maven (I am unaware of any in reality, but the M2E developers
> are mentioning this quite frequently)plugins assume that they are
> invoked from the command line. That means, in particular, that
> System.exit is called once Maven is done. Consequently, they consider
> use of resources as unproblematic: They acquire a lot, including
> memory and don't release it properly. The resources are released
> automatically by System.exit. But that doesn't work in M2E which runs
> as long as Eclipse does (meaning the whole day for Joe Average
> Developer) and invokes Maven (and the plugin with it) again and again.
>    M2E doesn't know whether a plugin (or, more precisely, a plugins
> goal) should run as part of an automatic build. For example, source
> and resource generators typicallyshould, artifact generetors typically
> should not. Consequently, a lot of unnnecessary plugins are invoked by
> the automatic build, slowing bdown the builder even more, while
> necessary goals are not. This is not what people expect and leads to
> invalid behaviour on the side of the developer. For exsmple, I keep
> telling my colleagues again and again that they shouldd invoke Maven
> manually, if the test suite depends on a generated property file.
> 
> But how should connectors fix this: I am partially speculating here,
> but my impression is this: When Maven is invoked as a builder, then it
> is modified by M2E to no longer invoke plugins directly. Instead,
> Maven invokes the plugins connector, which in turn invokes the plugin.
> The connector ought to know the plugin and decide, whether a goal must
> be invoked as part of the automatic build process or not. But that
> means, in particular:
> 
> M2E can invoke a plugin as part of the automatic build process if, and
> only if, there is a connector for the plugin, or you specially
> xonfigure the plugin. (More on that configuration later on.)
> 
> And that is the main problem we are currently facing: Connectors are
> missing for a lot of important plugins, for example the JAXB plugins,
> the JavaCC plugins, the antrun plugin, and so on. The philosophy of
> the M2E developers seems to be that time will cure thi s problem,
> which is why they are mainly ignoring it.See, for example,
> bug 350414, bug 347521, bug 350810, bug 350811, bug 352494, bug
> 350299, and so on. Since my first attempts with Indigo, I am unaware
> of any new connectors, although the lack of them is currently the
> biggest issue that most people have with M2E. Try a Google search for
> "m2e mailing list connector", if you don't believe me.
> 
> But even, if the developers werw right, they choose to completely
> ignore another problem: You can no longer use your own plugins in the
> Eclipse automatic builds, unless you create a connector for the
> plugin, or create a project-specific configuration. (Again, more on
> that confuguration in due time.)
> 
> At this point, one might argue: If you have written a plugin, it
> shouldn't be too difficult or too much work to write a connector as
> well. I'LL handle that aspect below.
> 
> First of all, regarding the configuration: Absent a suitable
> connector, there is currently only one possibility to use a plugin as
> part of the automatic build: You need to add a plugin-specific
> configuration snippet ike the following to your POM:
> 
> 
>    <plugin>
>    <groupid>org.eclipse.m2e</groupid>
>    <artifactid>lifecycle-mapping</artifactid>
>    <version>1.0.0</version>
>    <configuration>
>    <ifecyclemappingmetadata>
>    <pluginexecutions>
>    <pluginexecution>
>    <pluginexecutionfilter>
>    <groupid>org.codehaus.mojo</groupid>
>    <artifactid>javacc-maven-plugin</artifactid>
>    <versionrange>[2.6,)</versionrange>
>    <goals>
>    <goal>javacc</goal>
>    </goals>
>    </pluginexecutionfilter>
>    <action>
>    <execute></execute>
>    </action>
>    </pluginexecution>
>    </pluginexecutions>
>    </lifecyclemappingmetadata>
>    </configuration>
>    </plugin>
> 
> 
> 
> Neat, isn't it? And so short! This would advice M2E that I want the
> javacc-maven-plugin to run as a part of the automatic M2E build.
> 
> So far, I have tried to be as unbiased as posssible, but now to the
> points that drive me sick. (As if that were currently required...)
> 
>    The space required for the M2E configuration typically exceeds the
> actual plugin configuration by far! If there ever was a good example
> of POM pollution, here's a better one.
>    M2E insists in the presence of such configuration, regardless of
> whether I want the plugin to run or not.If it is missing, then the
> automatic builder won't work at all. There is no default handling, as
> was present in previous versions of M2E. (I won't discuss what the
> default should be, I'd just like to have any.)
>    The M2E configuration must be stored in the POM, or any parent
> POM. There is no other possibility, like the Eclipse preferences or
> some file in .settings. In other words, if you are using IDEA or
> NetBeans, but there is a single project member using Eclipsd, you
> still have to enjoy the M2E configuration in the POM. As bug 350414
> shows, there are a real lot of people who consider this, at best,
> ugly.
>    I tried to play nice and start creating connectors. But this
> simply didn't work: I am a Maven developer, not an Eclipse developer.
> And a connector is an Eclipse plugin. I'm not interested in writing
> Eclipse plugins. (Which Maven developer is?) But there is nothing like
> a template peoject or the like, only this well meant Wiki article,
> which doesn't help too much. For example, it assumes the use of Tycho,
> which only serves to make Eclipse programming even more complicated.
>    Thedesign of the connectors looks broken to me. Have a look at the
> AbstractJavaProjectConfigurator, which seems to be the typical
> superclass of a connector: It contains methods for configuring the
> Maven classpath, for adding source folders, for creating a list of
> files that have been created (or must be refreshed): These are all
> things that are directly duplicating the work of the Maven plugin and
> should be left to the Maven plugin, or Maven, alone. In other words:
>    Circumventing the Maven plugin is bad. Deciding whether to run or
> not should be left to the plugin, or Maven. (See, for example, the
> comment on "short-cutting" code generation on the Wiki page on writing
> connectors
>    .)
> 
> 
> To sum it all up:
> 
> I fail to see why we can't throw away the whole connector mess and
> replace it with a configurable Maven goal that should be run by the
> automatic build ? There is even a reasoable default: "mvn
> generate-resources". Let's reiterate the reasons for inventing
> connectors from above and compare it with this solution:
> 
>    Maven wouldn 't be invoked more frequently
>    If a single Maven execution takes too long, fix the plugins that
> don't do a good job at detecting whether they can short-cut. Ant still
> does a better job here, years after the invention of Maven 2.
>    If some plugins don't behave well with regard to resources,
> fix'em. If we can e´wait months or years for connectors, we might as
> well wait for bug fixes in plugins.
>    The question whether to run a plugin or not can be left to the
> Maven lifecycle, if we choose a lifecycle goal like
> "generate-resources" Maven knows perfectly well the plugins and goals
> to include or exclude.
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